1. Field of the Invention
This invention relates to articles of jewelry made of precious metal set with one or more gems and more particularly is directed to an improved utilization of the lost wax method of casting such articles of jewelry whereby the gem is set in the wax model and encased in the investment material enabling the article of jewelry to be cast in precious metal with the gem properly mounted in the setting when the casting is removed from the investment mold.
2. Description of the Prior Art
The desirability to reduce the dependence by manufacturers of articles of jewelry having gems set in precious metal on the high priced labor of skilled gem setters has long been recognized. In this regard, U.S. Pat. No. 4,154,282 granted to Herbert Kull on May 15, l979 utilizes the lost wax process for manufacturing such jewelry by forming the rubber mold in which the wax model is cast to accommodate the gem and positioning the latter in the rubber mold prior to closing the mold and injecting the wax. The wax model bearing the gem set therein is removed from the rubber mold and encased in the investment so that, after replacement of the wax by precious metal in accordance with the lost wax procedure, the cast article is removed from the investment mold with the gem preset in the metal and thereby eliminating the conventional step of setting the gem in the cast metal.
The conventional method of melting and removing the wax model and curing the investment mold preparatory to casting the precious metal therein is performed in an oven under reduced pressure and involves increasing the temperature by uniform increments to 700.degree. C. in 14 hours to completely remove the moisture and provide a hard, smooth interior mold surface against which the metal is cast. The Kull patent suggests that this preheating or curing of the investment mold be accomplished in 4 hours at temperatures not to exceed 500.degree. C.
In attempting to achieve the desired result of eliminating the need for a skilled gem setter to complete the article of jewelry, the method described in the Kull patent has been found to be inadequate in two respects, namely, (1) in the manner whereby the gem is set in the wax model and (2) the suggested procedure for curing the investment mold preparatory to casting the precious metal therein.
As to the first inadequacy, the step of properly positioning the gem as an insert in the open rubber mold and then closing the mold with a high degree of care so as not to displace the gem prior to injecting the wax has been found not only to be relatively time consuming but also unreliable, particularly when the jewelry design utilizes several relatively small gems in each article. Furthermore, any improper positioning of the gem during the molding of the wax model is not apparent until after the model is removed from the mold. Other imperfections in the wax model per se requires removal of the gems before discarding such defective model. All these all too frequent eventualities contribute to what is believed to be an unacceptable efficiency rate at this stage of the process.
As to the above mentioned second inadequacy, by limiting the curing of the investment material to a period of 4 hours at temperatures not to exceed 500.degree. C. required by Kull in order to prevent damage to the gems now retained in the investment mold after removal of the wax, the reduction in moisture content and hardening of the investment material has been found to be insufficient to enable the investment mold to withstand the injection of the molten metal which damages salient areas of the mold resulting in defective and unacceptable castings.
It is thus clear that the need to provide a practical, dependable, commercially feasible and efficient method of manufacturing cast precious metal jewelry with preset gems still exists.